The Moldovan Intelligence and Security Service said the gang was seeking €189,000 for the uranium, which police recovered during arrests on Thursday.

"A criminal group specialising in smuggling radioactive substances was uncovered," the service said in a statement. "Members of the group were found to be Moldovan citizens."

A video released by Moldovan authorities showed masked officers wrestling a man to the ground and using a Geiger counter to check radiation on a small package in his car.

The agency said it was attempting to establish the origins of the haul. It did not say exactly how much uranium had been recovered.

The incident is the latest in a series of radioactive smuggling incidents in the former Soviet republic, which has become the centre of an underground trade in materials believed to have been taken from Cold War-era stockpiles across the former USSR.

In February last year, Moldovan police and the FBI thwarted an attempt to sell highly radioactive caesium to Islamist terrorists, including Islamic State in Iraq and the Levant (Isil).

The seller had asked €2.5m for enough of the highly radioactive substance to contaminate several city streets with a dirty bomb.

Moldovan officials have said the most serious case they had encountered was in 2011, when a middle-man working for a Russian called Alexander Agheenco tried to sell bomb-grade uranium 235, along with weapon designs, to a Sudanese buyer.

Moldova's interior minister at the time said the gang was seeking €22m for the uranium.

Four Moldovans, a Russian, and a citizen of the unrecognised breakaway republic of Transnistria were arrested in that case, but the alleged mastermind, Agheenco, got away.

Moldovan authorities said at the time that they suspected Agheenco was a member of the Russian security services.

Other cases include the sale of a sawn-off piece of depleted uranium cylinder in 2010, and the attempted €12,000 sale of unenriched uranium in 2014.

Isil announced its intention to acquire nuclear materials as it rose to prominence in 2014.

It is believed to have seized around 90 pounds of low-grade uranium from Mosul University in Iraq after taking over the city that year, though its limited toxicity means its use would likely cause panic rather than serious harm.